Dental alloy



Aug. 4, 1936. R. L/COLEMAN ET AL I 2,050,040

' DENTAL ALLQY I Filed Sept. 27, 1934 Patented Aug, 4, 1936 PATENT" OFFICE ,VDENTAL ALLOY Richard L. Coleman and Keith Smith, Jr., West Hartford, Conn.

Application September 27, 1934, Serial No. 745,738

"3 Claims. (Cl. 75-165) This invention relates to alloys of precious metals (gold, silver, platinum and palladium), which are particularly adapted for the production of orthodontic appliances, such as stressbreakers, pins, posts, bands, lingual and palatal bars, and denture frames, although serviceable for other purposes, and which are commonly produced in the form of wire, but which may be cast or fabricated into strips andplates, inlays, bridges and the like industrial or dental products.

Such alloys previously produced for similar appliances have required careful and accurately? controlled heat treatment within narrow limits in order that they possess the necessary mechanical properties to permit fabrication and to ensure satisfactory service. The prior alloys if heated to high temperatures and cooled rapidly, as may occur when soldering, become soft and weak and the fabricated articles will not maintain their shape under the stresses of use. The old alloys if cooled slowlyf-rom high tempera tures, as in investments, or given a subsequent hardening heat treatment, which requires time and special equipment, are likely to become brittle, a frequent cause of breakage of the articles made therefrom.

The object of this invention is to provide products which have improved mechanical and thermal properties for the mentioned uses to which they may be put, that is alloys which are susceptible to heat treatment, to obtain the required strength, ductility, elasticity and hardness, with less danger of softening, over-hardening or embrittling, over .1. wider range of temperatures, as well as higher temperatures than the critical temperatures allowable with the precious metal alloys previously produced for similar purposes.

It is desirable that the optimum mechanical properties be developed at the relatively high temperatures to which these alloys are commonly subjected in the processes of fabrication thus obviating the necessity fora subsequent special heat treatment.

Susceptibility to heat treatment over a wider range of temperatures is desirable so that in cooling after soldering or other fabricating processes the fabricated article will remain within the heat treating temperature range for a longer time and, therefore, more nearly attain the maximum of its desirable properties.

We have discovered, and that is our inventive concept, that the reaction to heat treatment of dental alloys which include platinum and/or palladium, (for example platinum, without palladium, 12% to 30%, or palladium without platinum,

10% to 40%, or both platinum and palladium 12% to with copper (5% to 30%), and with or without gold (0% to-'75%) andsilver (0% to 50%), is so changed by the addition of a'small proportion of tin to 7 /g%) that such al- 6 loys are capable of having their mechanical properties improved by heating at higher temperatures, and over a wider range of temperatures than analogous alloys without tin. Variations, within the ranges specified, of the relative pro- 10 portions of the elements chosen for the particular article to be produced, are within the judgment of those skilled in this art.

A graphic example of the practical effect of the addition of tin in such alloys is illustrated 15 by Fig.1 wherein the lower row of numerals stand for degrees of temperatureFahrenheit-and the vertical series of numerals indicate tensile strength pounds per square inch.

Graph A represents the strength of an alloy 20 without tin after being first soft annealed by heing heated at 1650" F. and quenched and then i reheated at .the temperatures indicated and quenched. For the purpose of this specification soft annealing is to be understood as quenching 26 the alloy from a temperature high enough to relieve hardness caused by previous working or by heat treatment. This specimen alloy, composed of gold silver .8%, copper 9.4%, platinum 13.2%, palladium 11.6%, heated and cooled at 30 different temperatures between 1650 F. and 900 .F. varied in strength from about 83,000 lbs. to

85,000 lbs.

Graph B represents the strength, after being subjected to the same heat treatment, of a com- 35 position of the same elements with the addition of 1.5% of tin, the other elements, of course, being reduced proportionally. This shows that the tin content increased the strength of the alloy when heated at temperatures between 1650 F. and 900 F., the maximum increase of about 40% occurring at about 1200 F., a temperature.

[so high th t it would have practically no hardening effe t ;on the previously used alloys without tin. ,I

Graph 0 represents the condition for the same combination of elements with 3% of tin,-the other constituents being variedproportionally. This shows that between the same range of temperatures the strength increased from about 110,000 lbs. at 1650 F. to about 163,000 lbs. at 1150" R, an, increase of about 48%.

Fig. 2 graphically illustrates another example of the effect under the same conditions of heat treatment as those described in connection with 55 Fig. 1, of the employment of tin in a composition in which the proportions of the other elements are different from those above recited. With 55.2% of gold, 15.6% silver, 8.0% copper, 11.1% platinum, 10.1% palladium, and no tin, after heating between 1650 F. and 400 F. the strength ran from about 84,000 lbs. to only about 92,000 lbs., as shown by Graph D. By the addition of 1.3% of tin, the other elements being proportionally varied, under the same treatment between the same temperatures, the strength ranged from about 84,000 lbs. to about 115,000 lbs., as shown by Graph E. Graph E also shows that the alloy containing tin is very substantially hardenedby heating at all temperatures within the wide range of 400 F. to 1600 F.

The above are only examples, the relative proportions of the various elements may be varied within the limits previously mentioned, and a small amount of zinc (1% or 2% as a scavenger) or other metals that will not alter the basic properties of the alloy, may be added depending upon the use to which the alloy is to be put, as will be understood by those familiar with the art.

The attributes of the alloy described are such that the appliances made therefrom are not liable to be overhardened by any heat treatment likely to be employed in their fabrication. The reaction of the constituent metals is such that the alloy hardens efliciently throughout a much wider temperature range than do the alloys previously produced. In cooling after soldering or other heating operations, such as casting other metals about it, the alloy remains within its hardening temperature range longer and therefore is hardened to a. more efficient degree than is the case with prior alloys. On account of this property it is unnecessary to submit the alloy to any exactly controlled hardening heat treatment, or special heat treatment to develop the required strength and resilience, and this results in a very considerable saving of time and care, as well as in the elimination of special heat treating equipment. By reason of its qualities the alloy maintains its strength and resilience even after a number of solderings at high temperature, and its ductility is suflicient to permit all necessary manipulations and adjustments without weakening.

The invention claimed is:

1. A solid metal alloy for the fabrication of dental appliances, composed of 10% to 40% metal selected from the group platinum-palladium, 5% to 30% copper, /l;,% to 7 /2% tin, and 30% to 65% gold.

2. A solid metal alloy for the fabrication of dental appliances, composed of 12% to 30% of platinum, 5% to 30% copper, /1% to l /2% tin, and 30% to 65% gold.

3. A solid metal alloy for the fabrication of dental appliances, composed of 10% to 40% palladium, 5% to 30% copper, to l tin, 30

and 30% to 65% gold.

RICHARD L. COLEMAN. KEITH SMITH, JR. 

